Bag with thermal welded back seam

ABSTRACT

A bag having a thermal welded back seam is provided. The bag may be formed primarily of a thermoplastic material and may be in the form of a polywoven bag.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. Provisional Application Ser.No. 61/812,009, filed Apr. 15, 2013, the disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates generally to storage and transportcontainers such as bags. More particularly, the invention relates to abag formed primarily from a thermoplastic material and having a thermalwelded back seam. Specifically, the invention relates to such a bagwhich may be formed of a polywoven material.

2. Background Information

Storage devices come in many shapes, sizes and materials, many of whichare configured as a bag. To create the holding volume from a singlesheet of material, a manufacturing machine may fold or otherwise formmaterial to a desired shape. Many bags are sealed to ensure properholding of desired contents. While bags may contain a back seam, mostbags require a separate and distinct external additive, such as anadhesive, a hot melt glue or stitching to close or otherwise seal theback seam of the bag. To date, known bags have not been configured toseal the back seam without the need of such a distinct and separatematerial additive. Thus, a need exists for an improved bag.

SUMMARY

In one aspect, the invention may provide a bag comprising athermoplastic front panel; a thermoplastic back panel having left andright panel segments; an overlap of the left and right panel segments;and a thermal welded back seam which extends along the overlap and isfree of a hot melt glue which is different from the front and backpanels.

In another aspect, the invention may provide a bag comprising a tube ofthermoplastic sheet material which defines an interior chamber andincludes a front panel and a back panel having left and right panelsegments; wherein the front panel has an inner surface which faces theinterior chamber; an overlap of the left and right panel segments; athermal welded back seam which extends along the overlap and has aninner surface which faces the interior chamber; and broken welds alongthe inner surface of the back seam and the inner surface of front panel.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Embodiments of the invention illustrative of the best mode in whichApplicant contemplates applying the principles are set forth in thefollowing description and are shown in the drawings and are particularlyand distinctly pointed out and set forth in the appended claims.

FIG. 1A is a perspective view of a first sample embodiment of a baghaving an offset thermal welded back seam.

FIG. 1B is a perspective view of a second sample embodiment of a baghaving gussets and an offset thermal welded back seam.

FIG. 2 is a plan view of a bag having an offset thermal welded backseam.

FIG. 3A is a section view of the non-gusseted embodiment taken on line3A-3A of FIG. 2.

FIG. 3B is a section view of the gusseted embodiment taken on line 3B-3Bof FIG. 2.

FIG. 3C is an enlarged section view of the encircled portion of FIG. 3Ashowing the thermal welded back seam.

FIG. 4 is a plan view of a bag having a centered thermal welded backseam.

FIG. 5A is a section view of the non-gusseted with a centered thermalwelded back seam.

FIG. 5B is a section view of the gusseted embodiment with a centeredthermal welded back seam.

Similar numbers refer to similar parts throughout the drawings.

DETAILED DESCRIPTION

With primary reference to FIG. 1A, a sample embodiment of a bag is showngenerally at 10. Bag 10 may be a polywoven bag and comprises a frontpanel 24 (FIG. 3A) and a back panel 26 and has an offset thermal weldedback seam 28. Bag 10 is configured to hold a volume of bulk solid,liquid, or other material. Bag 10 is non-gusseted and has a firstlongitudinal or side edge 12 and an opposed second longitudinal or sideedge 14 spaced apart and defining an axial or width direction 16 therebetween. First and second side edges 12 and 14 are defined by a foldedpiece of a flexible sheet of a thermoplastic material, which may be apolywoven thermoplastic material. One thermoplastic material havingdesirable characteristics for the construction of bag 10 ispolypropylene, although other thermoplastic materials may be used toform the sheet material used to make the various panels of bag 10. Firstand second edges 12 and 14 may be generally parallel. Bag 10 has a firstend edge 18 and an opposed second end edge 20 and defining alongitudinal direction 22 there between. End edges 18 and 20 may begenerally parallel and may generally orthogonally intersect side edges12 and 14.

Front panel 24 and back panel 26 each have first side edges at oradjacent first side edges 12 and may be represented at 12, and secondside edges at or adjacent second side edges 14 and may be represented at14. In the sample embodiment, panels 24 and 26 are connected by thefolded thermoplastic material at longitudinal substantially parallelfolds which define side edges 12 and 14 and extend from end edge 18 toend edge 20. Front and back panels 24 and 26 define therebetween aninterior chamber 40 of bag 10. The ends 18 and 20 may be open at givenstage, or closed on one end and open on the other, or closed on bothends. Where both ends are open, the first end edges 18 of panels 24 and26 define therebetween a first entrance opening of interior chamber 40while the second end edges 20 of panels 24 and 26 define therebetween anopposed second entrance opening of interior chamber 40. When there aretwo entrance openings, the bag forms a flexible open-ended tube. One orboth of the entrance openings may be closed off by a seam or otherclosure. For example, front panel 24 and back panel 26 may be connectedalong their respective first end edges 18 and/or along their respectivesecond end edges 20 in conventional ways such as rolling, folding,sealing or any of various seaming methods to form a first end seam alongedge 18 and/or a second end seam along edge 20.

Thermal welded back seam 28 is disposed on the back panel 26 and usuallyextends longitudinally from end edge 18 to end edge 20 or from adjacentend edge 18 to adjacent end edge 20, and thus from adjacent one end edge18 and 20 toward the other of end edges 18 and 20. Back seam 28 iscreated by overlapping left and right back panel segments 30 and 32(FIGS. 1A, 3) of back panel 26 and welding them directly to each otherwithout the use of any type of hot melt glue, any adhesive, anystitching or other material which is different from the thermoplasticmaterial from which bag 10 is formed, and thus different from thethermoplastic front and back panels 24 and 26. Back seam 28 may beformed without any material other than the thermoplastic materialsforming left and right back panel segments 30 and 32. Back seam 28 maybe free of any type of hot melt glue, an adhesive, stitching or anymaterial which is different from the thermoplastic material from whichbag 10 is formed, and thus different from the thermoplastic front andback panels 24 and 26.

With primary reference to FIGS. 2, 3A and 3C, front panel 24 is acontinuous piece of material having a width 46 equal to or about equalto the distance between first and second side edges 12 and 14. Frontpanel 24 has an inner surface 24 a which faces and partially definesinterior chamber 40 and an outer surface 24 b which faces away fromchamber 40 and back panel 26. Back panel 26 has an inner surface 26 awhich faces and partially defines chamber 40 and outer surface 26 bwhich faces away from chamber 40 and front panel 24. Outer surfaces 24 band 26 b define an outer or exterior surface of bag 10. Right segment 32has a first or left edge which serves as a weld edge 34. Right segment32 is generally bound by end edge 18, end edge 20, first side edge 12and first weld edge 34. First side edge 12 and first weld edge 34 definetherebetween an axial normal right segment width 42 of right segment 32.Left segment 30 has a second or right edge which serves as a weld edge36. Left segment 30 is generally bound by first end edge 18, second endedge 20, second side edge 14, and second weld edge 36. Second edge 14and second weld edge 36 define therebetween an axial normal left segmentwidth 44 of left segment 30 which is significantly less than width 42,as shown in FIG. 2.

Back seam 28 extends axially from first weld edge 34 to second weld edge36, which define therebetween a weld width 38 (FIG. 3C) of a weldbetween a first welding surface 35 of a right portion of left segment 30and a second welding surface 37 of a left portion of right segment 32.These right and left portions overlap one another, thus forming anoverlap between left and right segments 30 and 32 such that weld edges34 and 36 are spaced apart and adjacent one another and typicallysubstantially parallel along their entire length. Although the sampleembodiment shows right segment 32 overlapped atop left segment 30, backseam 28 may, for example, be created with left segment 30 overlappedatop right segment 32. Width 38 of the weld in one sample embodiment isapproximately one inch, although this may vary especially depending onthe strength requirements of back seam 28. In the sample embodiment,first welding surface 35 is part of outer surface 26 b of left segment30 and second welding surface 37 is part of the inner surface 26 a ofright segment 32. (Similarly, in the embodiment discussed below, weldingsurface 135 is part of outer surface 126 b of left segment 130 andsecond welding surface 137 is part of the inner surface 126 a of rightsegment 132.)

Back seam 28 may provide a watertight seal and may be made entirely fromthe thermoplastic material which may form all or essentially all of bag10 in that no external substances need be added to create the bond ofback seam 28. Back seam 28 is typically thermally welded together usingonly heat and compression pressure (which may, for example, be appliedwith pinch rollers). Heating in the area where back seam 28 is to beformed melts the thermoplastic material in this area, particularly alongoverlapping surfaces 35 and 37. Welding surfaces 35 and 37 are typicallyheated in a range of about 100° F. to about 1450° F. although this mayvary depending on the thermoplastic material used. In particular, theweld is created by positioning first welding surface 35 and secondwelding surface 37 in an overlapping manner, heating welding surfaces 35and 37 of the overlap so that they melt, compressing the heatedoverlapping portions of segments 30 and 32 together, and cooling(actively or passively) the melted portions until they solidify, whichtypically occurs fairly rapidly. Preferably, the weld is continuousalong the entire length and width of the weld of back seam 28.

Formation of back seam 28 makes panel segments 30 and 32 become onecontinuous piece of material in the form of back panel 26, so that bag10 is a tube with open ends prior to being seamed along either end edge18 and 20. When welded properly, back panel 26 with the welded back seam28 will be as strong as a similarly sized continuous piece of the sheetmaterial. Thermal coalescence (that is, melting and cooling ofthermoplastic material to form seam 28) provides a back seam having thesame chemical properties as a solid piece of the sheet material.

Back seam 28 may be formed as described in the US patent applicationentitled “BACK SEAM WELDER AND METHOD OF OPERATION” which is filed onthe same date as the present application and is incorporated herein byreference. As detailed in said patent application, undesired incidentalwelds may be formed between the back seam and the front panel duringformation of the back seam. Thus, the back seam welder of saidapplication uses a weld breaker to break these incidental welds, thusforming broken welds 45 (FIGS. 3A, 3B, 3C, 5A, 5B) along inner surface26 a of back seam 28 and inner surface 24 a of front panel 24 directlyopposite back seam 28, or in the embodiment discussed further below,along inner surface 126 a of back seam 28 (panel segment 30) and innersurface 124 a of front panel 124 directly opposite back seam 28. Theincidental welds created during the formation of back seam 28 are formedof the same thermoplastic material of which the present bag is formed,including the front and back panels (and any gusset panels such as shownin the later embodiment). Thus, broken welds 45 are likewise formed ofthe same thermoplastic material of which the present bag is formed,including the front and back panels (and any gusset panels such as shownin the later embodiment).

Broken welds 45 extend inwardly respectively from inner surface 26 a,126 a of seam 28 (panel segment 30, 130) and inner surface 24 a, 124 aof the portion of front panel 24, 124 directly opposite seam 28. Thebroken welds 45 which extend inwardly from the inner surface of seam 28thus extend inwardly toward the broken welds 45 which extend inwardlyfrom the inner surface of the portion of the front panel directlyopposite seam 28. A portion of interior chamber 40 is directly betweenthe broken welds 45 which extend inwardly from inner surface 26 a, 126 aof seam 28 and the broken welds 45 which extend inwardly from innersurface 24 a, 124 a of the portion of the front panel directly oppositeseam 28.

A seam may be formed along first end edge 18, for instance, by abottomer device as conventionally known in the art. First end edge 18may be thermally welded or otherwise closed or sealed through otherknown conventional means. The seam along first end edge 18 may definewhat becomes the bottom of the bag in a manner sufficient to support thecontents within interior chamber 40. Similarly, the seam along secondend edge 20 may be heat welded, sealed or seamed with an adhesive,stitching or other means known in the art to form a seam along secondend edge 20 which may define what becomes the top of the bag and whichmay thus provide a sealed closure for the contents of chamber 40.

FIGS. 4 and 5A show back seam 28 generally centered along back panel 26,thus illustrating that back seam 28 may be disposed longitudinally alongthe back panel 26 at any position. The location of back seam 28 mayrelate to the contents to be contained by the bag and the desiredstrength properties of the bag. When back seam 28 is generally centered,left and right segments 30, 32 are generally equal in width (widths 42and 44 in FIG. 4) and each of widths 42 and 44 is generally slightlywider than one-half the width of front panel 24.

FIGS. 1B, 3B-C and 5B show a sample gusseted polywoven bag 110 having athermal welded back seam 128. Note that FIG. 5B shows that the bag isformed with seam 128 generally centered while FIGS. 1B and 3B show seam128 offset from center and FIG. 3C shows seam 128 regardless of position(as with seam 28). Bag 110 is substantially similar to bag 10 except forthe gusseted side edges and thus for the most part will be describedonly to the extent that bag 110 differs from bag 10. Bag 110 has a firstlongitudinal or side edge 112, 115 and a generally parallel secondlongitudinal or side edge 114, 117 defining therebetween an axial orwidth direction 116.

Bag 110 has a front panel 124 and a back panel 126 defining therebetweenan interior chamber 140. Front panel 124 has first and second opposedlongitudinal or side edges 115 and 117 which are at or adjacent the sideedges of bag 10. Likewise, back panel 126 has first and second opposedlongitudinal or side edges 112 and 114 which are at or adjacent the sideedges of bag 10. Front panel 124 has inner and outer surfaces 124 a and124 b analogous to surfaces 24 a and 24 b and thus has essentially thesame characteristics and relationships described above. Back panel 126has inner and outer surfaces 126 a and 126 b analogous to surfaces 26 aand 26 b and thus has the same characteristics and relationshipsdescribed above. Back panel 126 comprises a left segment 130 and a rightsegment 132 welded together by thermal welded back seam 128 along anoverlap of left and right segments 130 and 132 to form a weld along weldsurfaces 135 and 137, in the same manner as discussed above with respectto seam 28 being formed by an overlap of segment 30 and 32. Back panel126 is bound by edges 112, 114, 118, 120. Front panel 124 is bound byedges 115, 117, 118, 120.

Back seam 128 extends axially from first weld edge 134 to second weldedge 136, which define therebetween a weld width 38 (FIG. 3C) of theweld between first welding surface 135 of a right portion of leftsegment 130 and second welding surface 137 of a left portion of rightsegment 132. These weld edges, the weld and welding surfaces areanalogous to those of bag 10. Thus back seam 128 extends longitudinallyand axially in the same manner described above regarding bag 10.

One of the gusseted side edges of bag 110 includes two gusset panels 123(only one labeled) which extend inwardly respectively from side edges orlongitudinal outer folds 112 and 115 to an inner fold 119 which isfolded in the opposite direction from folds 112 and 115 and spacedinwardly of folds/edges 112 and 115 toward the opposite side edge 114,117. Inner fold 119 is thus adjacent and inward of side edge 112, 115.The other of the gusseted side edges of bag 110 includes two gussetpanels 125 (only one labeled) which extend inwardly respectively fromside edges or longitudinal outer folds 114 and 117 to an inner fold 121which is folded in the opposite direction from folds 114 and 117 andspaced inwardly of folds/edges 114 and 117 toward the opposite side edge112, 115. Inner fold 121 is thus adjacent and inward of side edge 114,117. All of folds 112, 115, 119, 114, 117 and 121 are generally parallelto one another and extend from end edge 118 to end edge 120 or fromadjacent edge 118 to adjacent edge 120. While bag 110 shows only twogusset panels in each gusseted side edge, it will be understood thatadditional panels and folds may be formed in each gusset.

Gusset panels 123 and 125 are formed of the same polywoven thermoplasticmaterial as front and back panels 124 and 126, and typically all ofthese panels 123-126 are formed from a single piece of a sheet of thepolywoven material which is folded at the above-noted folds to defineeach of the panels. Gusset folds 119 and 121 are spaced apart a normalaxial distance less than width 46 of bag 110. The cross section of eachgusseted side edge of the sample embodiment has a generally inwardfacing “W” shape. Other gusset shapes are contemplated, as bag 110 mayhave multiple aligned gusseted folds and gusset panels.

Preferably, prior to thermal welding, the back seam 28, 128 is formed ina manner creating a lap joint. However, other conventionally knownjoints as would be understood in the art to weld two pieces of materialtogether, such as a v-joint or butt joint, are contemplated. While backseam 28, 128 may be free from separate or different materials such asholt melt glue, stitching or an adhesive, branding or label materialsmay cover part of or the whole outer surface of the back panel, such asink or paper, yet do not heat seal and may be understood to form no partof the back seam 28, 128.

One advantage of bags 10, 110 is that a bag manufacturer may increaseproduction efficiency by thermal welding the back seam of the bag. A baghaving a thermal welded back seam removes manufacturing costs associatedwith adhesives, hot melt glue, stitching or other materials ordinarilyassociated with forming/sealing the back seam on a bag.

In the foregoing description, certain terms have been used for brevity,clearness, and understanding. No unnecessary limitations are to beimplied therefrom beyond the requirement of the prior art because suchterms are used for descriptive purposes and are intended to be broadlyconstrued.

Moreover, the description and illustration of the preferred embodimentof the invention are an example and the invention is not limited to theexact details shown or described.

1. A bag comprising: a thermoplastic front panel; a thermoplastic backpanel having left and right panel segments; an overlap of the left andright panel segments; and a thermal welded back seam which extends alongthe overlap and is free of a hot melt glue which is different from thefront and back panels.
 2. The bag of claim 1 wherein the front and backpanels define therebetween an interior chamber; the front panel has aninner surface which faces the interior chamber; the back seam has aninner surface which faces the interior chamber; and further comprisingbroken welds along the inner surface of the back seam and the innersurface of front panel.
 3. The bag of claim 1 wherein the front panelhas opposed first and second side edges and opposed first and second endedges; the back panel has opposed first and second side edges andopposed first and second end edges; the first and second side edges ofthe back panel are respectively adjacent the first and second side edgesof the front panel; the first and second end edges of the back panel arerespectively adjacent the first and second end edges of the front panel.4. The bag of claim 3 wherein the back seam extends from adjacent one ofthe first and second end edges of the back panel toward the other of thefirst and second end edges of the back panel.
 5. The bag of claim 4wherein the back seam extends from adjacent the one of the first andsecond end edges of the back panel to adjacent the other of the firstand second end edges of the back panel.
 6. The bag of claim 5 whereinthe back seam extends from the one of the first and second end edges ofthe back panel to the other of the first and second end edges of theback panel.
 7. The bag of claim 1 further comprising a first foldextending along the first side edges; and a second fold extending alongthe second side edges.
 8. The bag of claim 7 further comprising a thirdfold extending along the first side edges; and a fourth fold extendingalong the second side edges.
 9. The bag of claim 8 further comprising afifth fold extending along the first side edges; and a sixth foldextending along the second side edges.
 10. The bag of claim 7 whereinthe first fold defines the first side edges; and the second fold definesthe second side edges.
 11. The bag of claim 3 wherein the back seam issubstantially parallel to the first side edges and the second sideedges.
 12. The bag of claim 1 further comprising an interior chamberdefined between the front and back panels; a first entrance opening ofthe interior chamber adjacent the first end edges; and a second entranceopening of the interior chamber adjacent the second end edges.
 13. Thebag of claim 12 wherein the back seam extends from adjacent one of thefirst and second entrance openings toward the other of the first andsecond end openings.
 14. The bag of claim 1 further comprising aninterior chamber defined between the front and back panels; an entranceopening of the interior chamber adjacent the first end edges; an endseam extending from adjacent the first side edges to adjacent the secondside edges; wherein the back seam extends from adjacent one of theentrance opening and end seam toward the other of the entrance openingand end seam.
 15. The bag of claim 14 wherein the back seam extends fromthe entrance opening to the end seam.
 16. The bag of claim 1 wherein thefront and back panels are formed from a single sheet of thermoplasticmaterial.
 17. The bag of claim 16 wherein the thermoplastic material isa polywoven thermoplastic material.
 18. The bag of claim 1 wherein eachof the front and back panels is formed of a polywoven thermoplasticmaterial.
 19. The bag of claim 1 further comprising a first gussetextending along the first side edges; and a second gusset extendingalong the second side edges.
 20. A bag comprising: a tube ofthermoplastic sheet material which defines an interior chamber andincludes a front panel and a back panel having left and right panelsegments; wherein the front panel has an inner surface which faces theinterior chamber; an overlap of the left and right panel segments; athermal welded back seam which extends along the overlap and has aninner surface which faces the interior chamber; and broken welds alongthe inner surface of the back seam and the inner surface of front panel.